“The Most Beautiful iOS Design Kit Ever Made – by InVision”
mobile_design
MobileMozaic
A gallery of iPhone app designs
Viewport Sizes
Photoshop Grids
Photoshop grid templates for various screen sizes and common constraints.
Indigo Studio
An interaction design tool that helps you “create functional, animated UI prototypes while maintaining the focus on user experience at every step”
PlaceIt
This is awesome. Drag and drop an image into the browser to “generate product screenshots in realistic environments”.